metanephros

The metanephros, precursor of the definitive kidney, starts to develop.

The metanephros is the definite, permanent, but yet immature kidney.

The metanephros is derived from the posterior part of the opisthonephros.

The metanephros persists as the definitive adult kidney.

The failed induction will thereby cause the subsequent degeneration of the metanephros by apoptosis and other mechanisms.

The pronephros is the most immature form of kidney, while the metanephros is most developed.

The metanephrogenic blastema is moulded over the growing end of the latter, and becomes a part of the metanephros in this way.

The mesonephros and metanephros of amniotes are derived from different parts of the anamniote opisthonephros.

In amniotes the mesonephros is the embryonic kidney and a more complex metanephros acts as the adult kidney.

Kidney development, also called nephrogenesis, proceeds through a series of three successive developmental phases: the pronephros, mesonephros, and metanephros.

Key words: inductive tissue interaction, metanephros, apoptosis, signalling molecule, cell lineage, morphogenesis.

In 1949, Hyman wrote the opisthonephros "has used up the mesomere tissue from which in amniotes both mesonephros and metanephros come."

The renal tubules of the metanephros, unlike those of the pronephros and mesonephros, do not open into the Wolffian duct.

The 1st phase is the pronephric phase, the 2nd phase is the mesonephros and the 3rd and final stage is the metanephros.

Differentiation of the permanent kidney or the metanephros is critically dependent on inductive signalling between the nephrogenic mesenchyme and ureteric bud epithelium.

In the majority of vertebrates, the mesonephros persists into the adult, albeit usually fused with the more advanced metanephros; only in amniotes is the mesonephros restricted to the embryo.

In a developing embryo JAG1 expression is concentrated around the pulmonary artery, mesocardium, distal cardic outflow tract, major arteries, metanephros, branchial arches, pancreas, the portal vein, and otocyst.

Characteristic of nephrons of the metanephros are complicated tubular developments that result in the loop of Henle and the distal tubular association with the vascular pole of the renal corpuscle, the macula densa.

The mesonephros persists and forms the anterior portion of the permanent kidneys in fish and amphibians, but in reptiles, birds, and mammals, it atrophies and for the most part disappears rapidly as the permanent kidney (metanephros) begins to develop during the sixth or seventh week.

The failure of the metanephros to develop in cases of BRA and some cases involving unilateral renal agenesis (URA) is due primarily to the failure of the mesonephric duct to produce a ureteric bud capable of inducing the metanephric mesenchyme.